THE HAND (Fam, 2003)

The hand is the chief sensory organ of touch and is uniquely adapted for grasping. The radial side of the hand performs a pinch grip between the fingers and thumb, and the ulnar side performs a power grip between the fingers and palm. The bones of the hand can be divided into a central, fixed unit for stability and three mobile units for dexterity and power. The fixed unit consists of the eight carpal bones tightly bound to the second and third metacarpals (Figure 4-1). The three mobile units projecting from the fixed unit are:

FIGURE 4-1 BONES AND JOINTS OF THE WRIST AND HAND.

(From Hochberg H, Silman AJ, Smolen JS, et al., eds.: Rheumatology, 3rd ed. London: Mosby, 2003.)

The axis of the wrist and hand is an extension of the longitudinal axis of the radius and the third metacarpal, with the wrist in the neutral position. Because of the changing position of the wrist and hand with forearm pronation and supination, it is best to describe locations in the wrist awnd hand as volar (palmar), dorsal, radial, and ulnar rather than anterior, posterior, lateral, and medial. The hand has two arches: a longitudinal arch, in the mid palm from wrist to fingers, and a transverse arch across the mid palm. In the resting position, the fingers are normally slightly flexed at the metacarpophalangeal (MCP) and interphalangeal (IP) joints; this is referred to as the resting flexion cascade of the fingers.

WRIST JOINT

The radiocarpal joint is the proximal articulation of the wrist and is an ellipsoid joint between the distal radius and articular disk proximally and the scaphoid, lunate, and triquetrum distally (see Figure 4-1). The capsule is strengthened by the radiocarpal (dorsal and volar) ligaments. The articular disk, or triangular fibrocartilage of the wrist, joins the radius to the ulna. Its base is attached to the ulnar border of the distal radius, and its apex is attached to the root of the ulnar styloid process. The synovial cavity of the distal radioulnar joint is L-shaped and extends distally beneath the triangular fibrocartilage but is usually separated from the radiocarpal joint.

The radiocarpal, midcarpal distal radioulnar, and CMC joints do not communicate under normal circumstances. The presence of any communication, tested by wrist arthrography or MR arthrograms, implies torn ligaments or a torn capsule between them. The midcarpal joint is in continuity with the intercarpal joints except for the pisotriquetral articulation, which communicates with the radiocarpal joint (see Figure 4-1).

The carpal bones form a volar concave arch or carpal tunnel, with the pisiform and hook of the hamate on the ulnar side and the scaphoid tubercle and the crest of the trapezium on the radial side. The four bony prominences are joined by the flexor retinaculum (transverse carpal ligament), which forms the roof of the carpal tunnel. The distal flexion crease of the wrist marks the proximal border of the retinaculum. The palmaris longus (absent in 10% to 15% of the population) partly inserts into the flexor retinaculum and partly fans out into the palm, forming the palmar aponeurosis (fascia). The aponeurosis broadens distally and divides into four digital slips that attach to the finger flexor tendon sheath, MCP joint capsules, and proximal phalanges. There is usually no digital slip to the thumb (Markison, 1987).

Twenty-four extrinsic tendons cross the wrist and provide a unique combination of power and dexterity to the hand. Each tendon is enclosed for part of its course in a tenosynovial sheath. A wrist or finger tendon sheath is lined by an inner or visceral synovial layer that adheres closely to the tendon and an outer or parietal synovium that covers the inside of the fibrous tendon sheath. The visceral and parietal synovial tubes are united longitudinally by the mesotendon, a synovial fold that transmits vessels and nerves to the tendon. The mesotendon may disappear partially in some tendon sheaths and may be represented by threads or vinculae.

The common flexor tendon sheath encloses the long flexor tendons of the fingers (Strauch, 1985) (flexor digitorum superficialis and flexor digitorum profundus) and extends from approximately 2.5 cm proximal to the wrist crease to the mid palm. It runs with the flexor pollicis longus tendon sheath and the median nerve through the carpal tunnel (Figure 4-2). The tendon sheath of the little finger is usually continuous with the common flexor sheath. The flexor pollicis longus tendon to the thumb runs through a separate tenosynovial sheath but may join the common flexor sheath. The flexor carpi radialis is invested in its own short tendon sheath as it crosses the volar aspect of the wrist between the split radial attachment of the flexor retinaculum. It is separated from the carpal tunnel by the deep portion of the transverse carpal ligament. The flexor retinaculum straps down the flexor tendons as they cross at the wrist. The ulnar nerve, artery, and vein cross over the retinaculum but are covered by a fibrous band, the superficial part of the transverse carpal ligament, to form the ulnar tunnel, or Guyon canal.

FIGURE 4-2 FLEXOR TENDONS AND TENDON SHEATHS OF THE WRIST AND FINGERS.

(From Hochberg H, Silman AJ, Smolen JS, et al., eds.: Rheumatology, 3rd ed. London: Mosby, 2003.)

On the dorsum of the wrist, the extensor tendons pass through six tenosynovial, fibro-osseous tunnels beneath the extensor retinaculum: 1) the abductor pollicis longus and extensor pollicis brevis (usually in a single sheath), which constitute the first, most radial extensor compartment; 2) the extensor carpi radialis longus and brevis; 3) the extensor pollicis longus; 4) the extensor digitorum communis and extensor indicis proprius; 5) the extensor digiti minimi; and 6) the extensor carpi ulnaris, the most ulnar extensor compartment (Figure 4-3). Each tenosynovial sheath extends about 2.5 cm proximally and distally from the retinaculum. The extensor retinaculum, by its deep attachments to the distal radius and ulna, binds down and prevents bowstringing of the extensor tendons as they cross the wrist. The anatomic snuffbox corresponds to the depression between the extensor pollicis longus tendon and the tendons of the abductor pollicis longus and extensor pollicis brevis.

FIGURE 4-3 EXTENSOR TENDONS AND TENDON SHEATHS OF THE WRIST.

(From Hochberg H, Silman AJ, Smolen JS, et al., eds.: Rheumatology, 3rd ed. London: Mosby, 2003.)

Movements of the wrist include flexion (in the volar direction), extension, ulnar deviation, radial deviation, and circumduction. The intercarpal joints, particularly the lunate-capitate joint, contribute to wrist extension and flexion. Prime wrist flexors are the flexor carpi radialis, flexor carpi ulnaris, and palmaris longus. The prime extensors are the extensor carpi radialis longus and brevis and extensor carpi ulnaris.

CARPOMETACARPAL JOINTS

The first CMC joint is a saddle-shaped, very mobile articulation between the trapezium and the base of the first metacarpal. It allows 40° to 50° of thumb flexion–extension parallel to the plane of the palm and 40° to 70° of adduction–abduction perpendicular to the plane of the palm. These movements are important in bringing the thumb in opposition with the fingers. The second and third CMC joints are relatively fixed, but the fourth and fifth are mobile, allowing the fourth and fifth metacarpals to flex forward (15° to 30°) toward the thumb during power grip.

METACARPOPHALANGEAL JOINTS

The metacarpophalangeal (MCP) joints are ellipsoid joints that lie about 1 cm distal to the knuckles (metacarpal heads; see Figure 4-1). Their capsule is strengthened by the radial and ulnar collateral ligaments on the sides and by the volar plate on the volar surface. Because of the cam shape of the metacarpal head, the collateral ligaments are loose in the neutral position, allowing radial and ulnar deviations, but become tight in the flexed position, preventing side-to-side motion, referred to as a sagittal cam effect. The deep transverse metacarpal ligament joins the volar plates of the second to fifth MCP joints. The MCP joint of the thumb is large and has two sesamoid bones overlying its volar surface.

When the long extensor tendon of the digit reaches the metacarpal head, it is joined by the tendons of the interossei and lumbricals and expands over the dorsum of the MCP joint and digit to form the extensor hood or extensor expansion (Figure 4-4). The expansion divides over the dorsum of the proximal phalanx into an intermediate slip, inserted principally into the base of the middle phalanx, and two collateral slips inserted into the base of the distal phalanx (von Schroeder, 1997).

FIGURE 4-4 TENDON INSERTIONS OF THE FINGER AND EXTENSOR DORSAL EXPANSION (HOOD).

(From Hochberg H, Silman AJ, Smolen JS, et al., eds.: Rheumatology, 3rd ed. London: Mosby, 2003.)

The first MCP joint permits 50° to 70° flexion and 10° to 30° extension. Radial and ulnar deviations are limited to less than 10° to 20°. The other MCP joints allow 100° flexion, 10 to 20° extension, and 35° of radial and ulnar movement. The extensor pollicis brevis, extensor indicis proprius, extensor digitorum communis, and extensor digiti minimi extend the MCP joints (von Schroeder, 1993). The flexors are the flexor pollicis brevis, lumbricals, interossei, and flexor digiti minimi brevis, assisted by the long flexors. Radial and ulnar movements at the second to fifth MCP joints are a function of the intrinsic muscles.

INTERPHALANGEAL JOINTS

The proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints of the fingers and the IP joint of the thumb are hinge joints. Their capsules are strengthened by the collateral ligaments on the sides and by the volar plates on the volar surface, which serve to limit hyperextension, particularly at the PIP joints. Unlike the MCP joints, the radial and ulnar collateral ligaments remain taut in all positions, providing side-to-side stability throughout the range of movement.

The flexor tendon sheaths for the fingers enclose the tendons of the flexor digitorum superficialis and profundus to their insertions on the middle and distal phalanges, respectively. The sheaths extend from just proximal to the MCP joints to the bases of the distal phalanges (see Figure 4-2). The flexor sheath of the little finger is often continuous with the wrist common flexor tendon sheath. The thumb flexor pollicis longus tendon sheath extends proximally to the carpal tunnel. Segmental condensations, or annular pulleys, in the digital flexor sheaths prevent bowstringing of the tendons and are biomechanically critical for full digital flexion.

The PIP joints can hyperextend by 10° in young adults, and the joints allow 100° to 120° volar flexion. The DIP joints permit 50° to 80° volar flexion and 5° to 10° extension. The IP joint of the thumb allows 80° to 90° volar flexion and 20° to 35° extension. The flexor digitorum superficialis flexes the PIP joints, and the flexor digitorum profundus flexes the DIP joints of the fingers. The prime extensors are the interossei and the lumbrical muscles. The flexor pollicis longus flexes the IP joint of the thumb, and the extensor pollicis longus extends the joint.

INSPECTION

With the hands on the examining table, one makes a general assessment of age, inflammation, atrophy, deformity, and asymmetry. Age-related changes include prominent veins on the dorsum of the hand, mild atrophy of the intrinsic muscles, lentigines on the skin and osteoarthritic prominences at the CMC joint at the base of the thumb, and osteophytes at the DIP and PIP joints. Osteoarthritic changes are ubiquitous and eventually result in such enlargement of the small joints of the fingers and deformity (McMurtry, 1986).

Acute inflammation following trauma is characterized by regional swelling and erythema. In contrast, chronic inflammation has less swelling and erythema and is often associated with synovitis of the joints and/or tendons. Deformity of any or all joints occurs with all forms of arthritis, but the particular pattern of deformity can be characteristic of a specific type of arthritis and will aid in diagnosis. The deformity will mirror the patient’s functional limitations and will dictate treatment. Assessing the deformity, motion, and instability of each digit requires a systematic approach and thorough documentation. Detailed wrist palpation, including provocative testing for carpal instability, will allow the examiner to localize specific disorders.

ASSESSING SYNOVITIS OF THE JOINTS AND TENDONS

Chronic synovitis is best assessed on the dorsum of the hand and wrist, where the tendons and joints are close to the surface and have fewer constraining structures over them. Synovitis of the joints produces a diffuse swelling over the joint and is uniformly tense and sometimes warm to the touch (McMurtry, 1986). The PIP and DIP joints are palpated by compressing laterally and/or gently forcing the joint into hyperextension for tenderness (stress pain). Synovial thickening and effusion are assessed by the examiner using the thumbs and forefingers of both hands placed on opposite sides of the joint (Figure 4-5